1. Field of the Invention
The present invention relates to a double pipe connection structure and a method for connecting a double pipe, and particularly, relates to a double pipe connection structure and a method for connecting a double pipe in which caulking is used for connection of the double pipe.
2. Description of the Related Art
Conventionally, brazing has been usually used for connection of a double pipe. However, in this case, there have been problems that connection work takes time and effort, a degree of difficulty in connection is higher, process costs are comparatively high, and the like.
In this regard, for example, Japanese Patent Application Publication No. 2004-270928, or the like, has proposed a method of connecting a double pipe using caulking without brazing.
The related art disclosed in Japanese Patent Application Publication No. 2004-270928 provides a structure in which a bypass inner pipe having an O-ring mounted on an outer periphery thereof is inserted into an end of an inner pipe, an end part of this bypass inner pipe is inserted into a small diameter hole in a branch joint, an outer pipe having an O-ring mounted thereon is inserted into a large diameter hole coaxial with the small diameter hole in the branch joint, and a main body part that forms the large diameter hole is caulked to a depressed groove part formed on an outer periphery of the outer pipe.
However, in the above-mentioned prior art, since the bypass inner pipe formed separately from the double pipe is mounted on the double pipe, the bypass inner pipe causes increase in the number of components and increase in cost.
In addition, in order to mount the bypass inner pipe, the diameter of the inner pipe is expanded. Furthermore, in order to mount the O-ring on the outer pipe, the O-ring is mounted on the depressed groove formed by depressing a general part of the outer pipe inward.
For this reason, a flow passage area between the outer pipe and the inner pipe is narrowed, and flow resistance of a fluid flowing in the outer pipe increases.
Moreover, the outer pipe has a fixed diameter, a diameter of a large diameter hole in a joint member is limited, and flexibility of connection is low.